It is known that active matrix liquid crystal display devices are classified into two major types: a transmissive type and a reflective type.
In a transmissive liquid crystal display device, a backlight such as a cold cathode fluorescent lamp or a light-emitting diode (LED) is used, and optical modulation action of liquid crystal is utilized to select one of the two states: a state where light from the backlight passes through liquid crystal to be output to the outside of the liquid crystal display device and a state where light is not output to the outside of the liquid crystal display device, whereby a bright or dark image is displayed. Furthermore, those images are combined to display an image.
In a reflective liquid crystal display device, a state in which external light, that is, incident light is reflected at a pixel electrode and output to the outside of the device or a state in which incident light is not output to the outside of the device is selected using optical modulation action of liquid crystal, whereby a bright or dark image is displayed. Furthermore, those images are combined to display an image. Compared to the transmissive liquid crystal display device, the reflective liquid crystal display device has an advantage of low power consumption since the backlight is not used.
Patent Document 1 discloses a flexible active matrix light-emitting device in which a transistor and an organic EL element are provided over a film substrate.